U.S. patent number 4,316,256 [Application Number 06/108,340] was granted by the patent office on 1982-02-16 for thermostat with automatic heat/air conditioning changeover.
This patent grant is currently assigned to MicroComm Corporation. Invention is credited to Donald B. Hendricks, Robert M. Knight.
United States Patent |
4,316,256 |
Hendricks , et al. |
February 16, 1982 |
Thermostat with automatic heat/air conditioning changeover
Abstract
A microcomputer controlled digital thermostat has separate,
independent registers for storing heating control information and
cooling control information. On a periodic basis, the microcomputer
determines whether the furnace should be turned on, based upon a
temperature signal indicative of room temperature, a time-of-day
value indicative of the present time of day, and the stored heating
control information. If the furnace is already off and the
microcomputer determines that it should remain off, the
microcomputer then determines whether air conditioning is needed,
based upon the temperature signal, the time-of-day value, and the
stored cooling control information.
Inventors: |
Hendricks; Donald B.
(Bloomington, MN), Knight; Robert M. (Greenwood, MN) |
Assignee: |
MicroComm Corporation
(Minneapolis, MN)
|
Family
ID: |
22321647 |
Appl.
No.: |
06/108,340 |
Filed: |
December 31, 1979 |
Current U.S.
Class: |
700/278; D10/50;
236/46R; 700/16; 165/238 |
Current CPC
Class: |
G05D
23/1917 (20130101); F23N 5/022 (20130101); F23N
2223/08 (20200101) |
Current International
Class: |
F23N
5/02 (20060101); G05D 23/19 (20060101); F23N
005/20 (); H05B 001/02 () |
Field of
Search: |
;364/505,557,104,418,107
;236/46R,78A |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Wise; Edward J.
Attorney, Agent or Firm: Kinney, Lange, Braddock, Westman
and Fairbairn
Claims
What is claimed is:
1. Temperature control apparatus for providing heating control
signals for controlling heating apparatus and cooling control
signals for controlling cooling apparatus, the temperature control
apparatus comprising:
temperature sensing means for providing a temperature signal
indicative of a sensed temperature;
time-of-day means for providing a time-of-day value;
means for storing heating control information including heating
time values and associated heating control temperature values;
means for storing cooling control information; and
control means for providing the heating control and cooling control
signals, wherein the control means periodically makes a heating
control determination, based upon the time-of-day value, the
temperature signal, and the stored heating control information, to
provide a heating control signal which
(a) turns the heating apparatus on,
(b) turns the heating apparatus off,
(c) leaves the heating apparatus on, or
(d) leaves the heating apparatus off; and wherein only if the
heating control determination leaves the heating apparatus off, the
control means makes a cooling control determination based upon the
time-of-day value, the temperature signal, and the cooling control
information, to provide a cooling control signal which
(e) turns the cooling apparatus on,
(f) turns the cooling apparatus off,
(g) leaves the cooling apparatus on, or
(h) leaves the cooling apparatus off.
2. The apparatus of claim 1 wherein the control means makes its
heating control determination by comparing the time-of-day value
with the heating time values stored to select a heating control
temperature value, and comparing the temperature signal and the
selected heating control temperature value.
3. The apparatus of claim 2 wherein the cooling control information
includes a turn-off time value indicative of a time when the
cooling apparatus is to be turned off.
4. The apparatus of claim 3 wherein the cooling control information
includes a turn-on time value indicative of a time when the cooling
apparatus becomes operational, and a cooling control temperature
value.
5. The apparatus of claim 4 wherein the control means makes a
cooling control determination as a function of the turn-off time
value, the turn-on time value, the cooling control temperature
value, the time-of-day value, and the temperature signal.
6. The apparatus of claim 5 wherein the turn-off time value has a
state whch indicates that the cooling apparatus is to remain
continuously off.
7. The apparatus of claim 5 wherein the control means will not
provide a cooling control signal to turn on the cooling apparatus
if the turn-off temperature value indicates that the cooling
apparatus is to remain continuously off.
8. The apparatus of claim 5 wherein the control means will provide
a cooling signal to turn on the cooling apparatus during a time
period when the turn-on and turn-off time values indicate the
cooling apparatus is to be off, if the temperature signal indicates
a sensed temperature above a predetermined value.
9. Temperature control apparatus for providing heating control
signals for controlling heating apparatus and cooling control
signals for controlling cooling apparatus, the temperature control
apparatus comprising:
temperature sensing means for providing a temperature signal
indicative of a sensed temperature;
time-of-day means for providing a time-of-day value;
means for storing heating control information including heating
time values and associated heating control temperature values;
means for storing cooling control information independent of the
heating control information; and
control means for providing the heating control signals and the
cooling control signals, wherein the control means periodically
makes a heating control determination bsed upon the time-of-day
value, the temperature signal, and the heating control information,
and makes a cooling control determination only if the heating
control determination indicates that operation of the heating
apparatus is not required, the cooling control determination being
based upon the time-of-day value, the temperature signal, and the
cooling control information.
10. The apparatus of claim 9 wherein the control means makes its
heating control determination by comparing the time-of-day value
with the heating time values stored to select a heating control
temperature value, and comparing the temperature signal and the
selected heating control temperature value.
11. The apparatus of claim 10 wherein the cooling control
information includes a turn-off time value indicative of a time
when the cooling apparatus is to be turned off.
12. The apparatus of claim 11 wherein the cooling control
information includes a turn-on time value indicative of a time when
the cooling apparatus becomes operational, and a cooling control
temperature value.
13. The apparatus of claim 12 wherein the control means makes a
cooling control determination as a function of the turn-off time
value, the turn-on time value, the cooling control temperature
value, the time-of-day value, and the temperature signal.
14. The apparatus of claim 13 wherein the turn-off time value has a
state which indicates that the cooling apparatus is to remain
continuously off.
15. The apparatus of claim 13 wherein the control means will not
provide a cooling control signal to turn on the cooling apparatus
if the turn-off temperature value indicates that the cooling
apparatus is to remain continuously off.
16. The apparatus of claim 13 wherein the control means will
provide a cooling signal to turn on the cooling apparatus during a
time period when the turn-on and turn-off time values indicate the
cooling apparatus is to be off, if the temperature signal indicates
a sensed temperature above a predetermined value.
17. A method of providing heating control signals and cooling
control signals for controlling heating apparatus and cooling
apparatus, the method comprising:
providing a temperature signal indicative of sensed
temperature;
storing heating time values and associated heating control
temperature values for use in controlling heating;
storing cooling time values and an associated cooling control
temperature value for use in controlling cooling independent of the
heating time values and associated heating control temperature
values;
providing a time-of-day value indicative of time-of-day;
periodically comparing the time-of-day value with stored heating
time values to select one of the associated heating control
temperature values;
comparing the temperature signal with the selected heating control
temperature value to determine an appropriate heat control
signal;
determining, only if the temperature signal exceeds the heating
control temperature value, whether the cooling apparatus is in
operation; and
comparing the temperature signal and the cooling control
temperature value, if cooling apparatus is in operation, to
determine an appropriate cooling control signal.
18. The method of claim 17 wherein determining whether cooling
apparatus is in operation occurs only if the heating apparatus is
already turned off, and the temperature signal exceeds the heating
control temperature value.
19. The method of claim 17 and further comprising:
storing an indication of whether the cooling apparatus is to be
continuously off at all hours during the day.
20. The method of claim 19 wherein determining whether the cooling
apparatus is in operation comprises:
determining from the stored indication whether the cooling system
is to be continuously off at all hours during the day; and
if the cooling apparatus is to be on during at least a portion of
the day, comparing the time-of-day value and the cooling time
values to determine whether the cooling apparatus is in
operation.
21. The method of claim 20 and further comprising:
providing a cooling control signal to turn on the cooling apparatus
if the temperature signal indicates a temperature greater than a
predetermined maximum temperature value and if the stored
indication indicates that the cooling apparatus is to operate
during at least a portion of the day.
Description
REFERENCE TO CO-PENDING APPLICATION
Reference is hereby made to our co-pending patent application
entitled "Digital Thermostat" which was filed on even date with
this application, and which is assigned to the same assignee as the
present application.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to temperature control apparatus. In
particular, the present invention relates to a thermostat which
automatically provides changeover between heating and cooling.
2. Description of the Prior Art
With the dramatic increase in energy costs in recent years, and the
growing concern over the availability of fuels, increased attention
has been focused upon energy conservation. The reduction of energy
consumption in home heating has been a topic of widespread
interest.
Significant energy saving in home heating can be achieved by the
use of temperature setback at one or more periods during each day.
For example, by decreasing the control temperature setting of a
thermostat during sleeping hours and during times of day when no
one is at home, significant energy savings can be achieved. Clock
thermostats which provide at least one setback period have been
available for many years. Until recently, these clock thermostats
have generally been of a mechanical or electromechanical type.
With the recent development of microprocessors and microcomputers,
computerized thermostats which automatically provide two or more
setback and setup temperature periods have been developed. Among
manufacturers of computerized thermostats are Autotronics, Inc.,
Control Pak Corporation, Honeywell, Inc., Micro Display Systems,
Inc., PSG Industries, Inc., RapidCircuit Corp., and Texas
Instruments. A description of computerized thermostats available
from these manufacturers may be found in Popular Science,
"Computerized thermostats program your comfort and save on energy
costs", pages 104-106 (October 1979).
Other digital thermostats or process control apparatus are
disclosed in the following U.S. patents:
Bunting: No. 3,912,913
Stephenson: No 4,001,557
Marooka et al: No. 4,004,138
Hall: No. 4,071,745
Wong: No. 4,079,366
Wyland: No. 4,110,632
Balduzzi et al: 4,162,036
In Bunting Pat. No. 3,912,913, a process control apparatus is
disclosed which includes a digital computer. Digital temperature
values from a temperature register are compared with values from a
temperature sensor. A program which may be coded on a punch card or
tape is read by a program reader and is used to control the
arithmetic unit and provide selection of the proper temperature
from the temperature register at the appropriate times.
The Stephenson Pat. No. 4,001,557 shows a digital process
controller having a timing clock which is used in conjunction with
programmable read only memories. A specific embodiment shown by
Stephenson shows temperature being varied as a function of time,
together with auxiliary control of a vacuum pump and a gas
pump.
In the Marooka et al Pat. No. 4,004,138, a temperature control for
a steel furnace is shown. The control utilizes various arithmetic
units and a temperature decision unit to control temperatures in
various zones of the steel furnace.
The Hall Pat. No. 4,071,745 shows a microprocessor controlled
electronic thermostat. The values of the reference temperatures and
times are programmable and changeable by the user. In addition,
hysteresis and anticipation values are stored. Zone control of
multiple zones is also illustrated in the Hall patent.
The Wong Pat. No. 4,079,366 shows a digital thermostat which
includes digital memories, a keyboard and a display. The user may
program in any desired temperature and time. Hysteresis is
adjustable in the digital thermostat of the Wong patent. In
addition, day off selectors are provided so that weekends can have
a different time/temperature program.
The Wyland Pat. No. 4,110,632 shows a device which monitors indoor
and outdoor temperatures together with a time count from a
seven-day counter. The purpose of the device is to disconnect
selective loads when conditions of peak electrical use are likely
to occur.
The Balduzzi et al Pat. No. 4,162,036 shows a solid state
thermostat having a pair of potentiometers R.sub.d and R.sub.v
controlled by knobs 13 and 14 to provide set points for high and
low temperatures. One or the other of these two potentiometers is
switched into a bridge by switches S1 and S2. These switches are
controlled by flipflop FF4, which in turn is controlled by Clock 1
and Clock 2. When one of the clock settings is reached, it triggers
FF4 which in turn selects the appropriate switch S1 or S2.
Although there has been considerable recent activity in the
development of digital computerized thermostats, there is a
continuing need for improvement. One shortcoming of both the prior
art electro-mechanical thermostats and the more recently developed
digital computerized thermostats is that the changeover from
heating to air conditioning and vice versa is performed manually by
a control switch or the like. This is inconvenient particularly in
those climates having hot days and cool nights, where air
conditioning is required during the daylight hours and heating is
required at night.
In addition, in the prior art digital computerized thermostats, the
air conditioning program has typically not been independent of the
heat program. As a result, when the user manually switches from a
heat program to an air conditioning program, re-programming of the
thermostat has been required and/or the heat program has been lost.
Similar problems occur each time a changeover is made back from the
air conditioning program to the heat program.
SUMMARY OF THE INVENTION
The present invention is an improved temperature control apparatus
which provides automatic changeover between heating and cooling, so
that the control apparatus controls both heating apparatus (e.g. a
furnace) and cooling apparatus (e.g. air conditioning) without
requiring a manual switching or reprogramming of heating or cooling
control information.
The temperature control apparatus of the present invention includes
means for storing heating control information for use in
controlling the heating apparatus and means for storing cooling
control information for use in controlling the cooling apparatus.
Temperature sensing means provide a temperature signal indicative
to a sensed temperature, and time-of-day means provide a
time-of-day value.
Control means provide heating and cooling control signals for
controlling the heating apparatus and the cooling apparatus,
respectively. The control means periodically makes a heating
control determination based upon the time-of-day value, the
temperature signal, and the stored heating control information. As
a result of the heating control determination, the control means
provides a heating control signal which (a) turns the heating
apparatus on; (b) turns the heating apparatus off; (c) leaves the
heating apparatus on; or (d) leaves the heating apparatus off. If
the control means has made a heating control determination to leave
the heating apparatus off, the control means then makes a cooling
control determination based upon the time-of-day value, the
temperature signal, and the cooling control information. As a
result of the cooling control determination, the control means
provides a cooling control signal which (e) turns the cooling
apparatus on; (f) turns the cooling apparatus off; (g) leaves the
cooling apparatus on; or (h) leaves the cooling apparatus off.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of the programmable electronic
thermostat of the present invention.
FIG. 2 is an electrical schematic diagram of the programmable
electronic thermostat of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
In FIG. 1, thermostat 10 of the present invention includes
generally rectangular housing 12 which is typically mounted on a
wall within the house or building whose temperature is being
controlled by thermostat 10. Front face plate 14 of thermostat 10
includes a two-digit display 16 and a plurality of membrane
switches or keys including TIME SET key 18, HEAT SET key 20, AC SET
key 22, AC OFF key 24, and TEMPERATURE "50", "60", "70" and "80"
keys 26a, 26b, 26c and 26d, respectively.
The membrance switches are used to both program the thermostat
(i.e. enter and store time and temperature settings) and for
program recall, so that the user can view, through display 16, the
stored time/temperature settings.
FIG. 2 is a schematic diagram of a preferred embodiment of the
thermostat of the present invention. The circuitry shown in FIG. 2
is mounted within housing 12 of FIG. 1. As shown in FIG. 2, the
thermostat is capable of controlling a furnace, an air conditioning
system, and a blower fan.
Terminals 28 and 30 are connected in series with the valve relay or
fan furnace relay of the furnace. In the embodiment shown in FIG.
2, terminal 28 is color coded RED, and terminal 30 is color coded
WHITE. Power for the thermostat, in the form of 24 volt AC
electrical power from the furnace electrical system is derived from
terminals 28 and 30.
Terminal 32, which is color coded YELLOW, is connected to the air
conditioning system. Terminal 34, which is color coded GREEN, is
connected to the blower fan control. Terminals 32 and 34 are used
when the house or building also has a central air conditioning
system.
The input power from terminals 28 and 30 is rectified and filtered
by a full wave rectifier bridge power supply circuit including
diodes 36, 38, 40 and 42, current limiting resistor 44, filter
capacitor 46, bleedback resistor 48, diode 50, and Zener diode 52.
The voltage V+ necessary for operation of the electronic circuitry
of thermostat 10 is established between the cathode and anode of
Zener diode 48. In a preferred embodiment of the present invention,
voltage V+ is approximately 5 volts. Because the current required
to operate the thermostat is very low (on the order of a few
milliamperes), the furnace valve relay connected in series with
terminals 28 and 30 is not actuated.
Connected between terminals 28 and 30 is metal oxide varistor (MOV)
54. The purpose of MOV 54 is to suppress spikes due to relay turn
on and other electrical noise.
The thermostat of FIG. 2 also includes backup power supply 56 in
the event of loss of input power at terminals 28 and 30. In one
preferred embodiment, backup power supply 56 includes a
battery.
Operation of the thermostat is controlled by microcomputer 57. As
shown in FIG. 2, microcomputer 57 includes V.sub.CC and V.sub.XX
terminals (which are connected to the power supply voltage V+);
terminals V.sub.SS and TEST (which are connected to ground); an
MCLR input, an OSC input, an RTCC inputt, and ports A0-A3, C0-C3,
C5-C7 and a-g.
Microcomputer 57 receives input signals from the face plate
switches 18, 20, 22, 24 and 26a-26d of face plate 14 through
flexible conductor 58 and ports A0-A3. Microcomputer 57 multiplexes
the eight switches of face plate 14 by means of signals from ports
C0 and C1.
Microcomputer 57 also receives a temperature signal from
temperature sensing circuit 59. The temperature signal, which is
supplied to the RTCC input of microcomputer 57, has a frequency
which is a function of sensed temperature.
In the embodiment shown in FIG. 2, temperature sensing circuit 59
includes thermistor 60, potentiometer 62, resistor 64, capacitors
66 and 68 and timer 70. Thermistor 60 is exposed to the room
environment through a hole (not shown in FIG. 1) in housing 12. The
resistance of thermistor 60 varies as a function of sensed
temperature.
In the preferred embodiments shown in FIG. 2, timer 70 is a 555
type integrated circuit timer. The output of timer 70 is a
temperature signal which is supplied to the RTCC input of
microcomputer 57. As the temperature increases, the temperature
signal from timer 70 increases. Conversely, as room temperature
decreases, the frequency of the signal decreases. Microcomputer 56
counts the pulses of the temperature signal from timer 70 and
thereby converts the frequency of the temperature signal to a
digital temperature value.
Based upon signals received from the switches or keys of face plate
14 and the output signal of timer 70, microcomputer 57 controls
display 16 through ports a-g and resistors 72a-72g. Display 16 is
multiplexed by microcomputer 57 by signals supplied to the A1 and
A2 inputs of display 16. The A1 input is controlled by the C0 port
of microcomputer 57 through resistor 74 and transistor 76.
Similarly, the A2 input of display 16 is controlled by
microcomputer 57 through port C1, resistor 78, and transistor
80.
Microcomputer 57 controls current flow between terminals 28 and 30,
and therefore the furnace valve relay, by means of heat control
circuit 82 connected to port C2 of microcomputer 57. As shown in
FIG. 2, heat control circuit 82 includes transistors 84, 86 and 88,
and resistors 90, 92 and 94. Transistor 88 has its
emitter-collector current path connected in parallel with current
limiting resistor 44. In normal operation, transistor 88 is turned
off, so that all current flow passes through current limiting
resistor 44. When transistor 88 is turned on, on the other hand, a
large current flow is permitted, which is sufficient to actuate the
furnace valve relay.
Current flow between the RED terminal 28 and YELLOW terminal 32,
and therefore operation of the air conditioning system, is
controlled by microcomputer 57 through AC control circuit 94
connected to port C3. AC control circuit 94 includes resistor 96,
transistor 98, diode 100, and reed switch 102. Normally open
contacts 104 of reed switch 102 are connected between terminals 28
and 32. When current flows through coil 106 of reed switch 102,
contacts 104 are closed, thereby closing the circuit between
terminals 28 and 32, and actuating the air conditioning system.
As shown in FIG. 2, current flow between GREEN terminal 34 and RED
terminal 28 is controlled by a normally open FAN ON switch 108.
When switch 108 is closed, current flow between terminals 28 and 34
is permitted, thereby causing constant operation of a blower fan.
Switch 108, which is not shown in FIG. 1, is preferably located on
the lower portion of housing 12 and is controllable by the
user.
Resistor 110 and capacitor 112 are connected to the MCLR input of
microcomputer 57. Upon initial power up of the thermostat, the
signal at the MCLR input causes microcomputer 57 to initialize the
various registers containing temperature and time settings and to
cause display 16 to display a flashing "00" indicating power up
conditions to the user.
Connected to the OSC input of microcomputer 57 are resistor 114 and
capacitor 116. The values of resistor 114 and capacitor 116
determine the frequency of internal clock signals used by
mirocomputer 57.
Contacts 118 are connected between port C5 of microcomputer 57 and
ground. When the thermostat is intended for use with 60 Hz power,
contacts 118 are open, and the port C5 is not grounded. When, on
the other hand, 50 Hz input power is to be used, contacts 118 are
soldered closed. In this manner, the same thermostat circuit can be
used for both 50 Hz and 60 Hz applications, with one minor
alteration in the factory or in the field.
Port C6 of microcomputer 57 is connected to WHITE terminal 30
through diode 120. The signal at port C6 is a half wave rectified
AC signal which is used by microcomputer 57 to keep track of the
time of day. By counting cycles of the signal at port C6 and
knowing whether the input power is 50 or 60 Hz (by monitoring port
C5), microcomputer 57 maintains time of day for use in its control
function.
Port C7 is connected to the anode of diode 50 (and one terminal of
filter capacitor 46). The signal at port C7, therefore, indicates
whether AC power is present between terminals 28 and 30. As long as
AC power is present, filter capacitor 46 is charged and the signal
at port C7 is high. In the event of a loss of AC input power,
filter capacitor 46 discharges and the signal at port C7 goes low.
Diode 50 prevents current from backup power supply 56 from
recharging filter capacitor 46 in the event of a loss of AC power,
while permitting backup power supply 56 to supply voltage V+
necessary to maintain microcomputer 57 in operation.
In the event of loss of AC power, microcomputer 57 turns off heat
control circuit 82 and AC control circuit 94, thereby minimizing
the current draw from backup power supply 56. The current draw from
backup power supply 56 when AC power is lost is relatively
low--only that which is required to preserve the contents of the
memories within microcomputer 57.
During normal operation, microcomputer 57 controls operation of the
furnace as a function of the time of day, the stored
time/temperature settings (which were entered through the switches
of face plate 14) and the temperature signal supplied by
temperature sensing circuit 59. In a preferred embodiment of the
present invention, up to four different time and temperature
settings may be entered and stored within microcomputer 57.
In the case of air conditioning, a turn on time, a turn off time
and a desired temperature are stored. Control of air conditioning
is between the turn-on time and the turn-off time. The stored times
and temperatures for air conditioning are independent of the stored
time/temperature settings for heating.
The present invention provides entry and recall of time and
temperature settings by means of switches 18, 20, 22, 24 and
26a-26d, together with display 16. The number of switches or keys
required to enter and recall settings is limited to only eight
keys, thereby reducing cost of the thermostat of the present
invention and simplifying entry and recall.
As discussed previously, when thermostat 10 is turned on (after
installation and after each loss of voltage V+), the MCLR signal
causes microcomputer 57 to initialize all temperature and time
setting registers and to cause a flashing "00" to be displayed on
display 16. This indicates to the user that thermostat 10 is in a
power up phase after a loss of power.
The first operation which must be performed by the user is to enter
the time of day (to the nearest hour) into a time-of-day register
designated "HO" (for "hour"). The user contacts the TIME SET key
18, holds key 18 for a time in excess of six seconds. Microcomputer
57 requires that TIME SET key 18 (and any of the other keys) be
maintained for greater than six seconds in an ON state in order to
make a change in stored values within the memory of microcomputer
57.
In order to enter and store the time of day, the user presses and
holds TIME SET key 18 in an ON condition until "HO" is displayed on
display 16. As key 18 continues to be held ON, the time of day
appears and begins to increase incrementally from "1" (for 1 a.m.)
toward "24" for (12 p.m.) until the operator releases TIME SET key
18. Whatever hour (from "1" through "24") which is displayed on
display 16 at the moment that TIME SET key 18 is stored in a time
of day register by microcomputer 57. Thereafter, microcomputer 57
updates the time of day register based upon the AC input received
at port C6 and based upon whether the AC input is 50 or 60 cycles,
as indicated by port C5.
In the present invention, the time of day is maintained only to the
nearest hour. This is sufficient accuracy for controlling
temperatures in a home or building, and permits the use of a
two-digit display, rather than requiring four digits.
In order to recall and view the time of day, the user simply
presses and then releases TIME SET key 18. As long as the time
which key 18 is held is less than 3 seconds, microcomputer 57
causes the letters "HO" to appear on display 16. Microcomputer 57
then causes the time of day to appear on display 16.
Once the time of day has been stored, microcomputer 57 causes
display 16 to display room temperature, as sensed by thermistor 94.
Room temperature continues to be displayed except when a key has
been pressed to enter or recall settings. This differs from the
prior art digital clock thermostats, which normally display time of
day. This feature of the present invention is particularly
advantageous, since it is room temperature and not the time of day
which is of foremost concern of the user when checking the
thermostat. It is inconvenient to have to press a key or switch in
order to determine room temperature, as in the prior art
devices.
After the user has set the time of day, the next operation to be
performed is to set the time/temperature registers for controlling
heating. In a preferred embodiment of the present invention, a
total of four different registers, designated H1-H4, are provided
for storing up to four different time/temperature settings. The
user enters the desired settings into registers H1-H4 by means of
HEAT SET key 20 and TEMPERATURE keys 26a-26d.
To set the first time/temperature register H1, the user presses and
holds HEAT SET key 20. Microcomputer 57 causes display 16 to
display "H1". Three seconds later, if the user is still holding
HEAT SET key 20, a time will begin to be displayed on display 16.
Assuming that H1 has not been previously set, the time displayed is
initially "00". As the user continues to hold HEAT SET key 20 for
three more seconds, the displayed time will begin to increment from
"00" upward toward "24". When the user releases HEAT SET key 20,
the time displayed on display 16 at the instant when HEAT SET key
20 was released is stored in register H1.
Upon release of HEAT SET key 20, microcomputer 57 again causes
display 16 to display the room temperature. The user then presses
and releases HEAT SET key 20, and presses and holds one of the four
TEMPERATURE keys 26a-26d. Each of these four keys represents one
decade of temperatures in .degree.F. For example, if the user
desires a temperature of 68.degree. F. for H1, he presses
TEMPERATURE key 26b. This causes display 16 to begin displaying
temperatures beginning with "60" and moving incrementally upward to
"69" as TEMPERATURE key 26 continues to be held. When the user
releases TEMPERATURE key 26b, the temperature then being displayed
on display 16 is stored in memory by microcomputer 57 in register
H1.
Similar operation is provided by keys 26a, 26c and 26d. In the
event the user continues to hold a particular TEMPERATURE key until
the highest temperature in the decade has been reached, the
displayed temperature returns to the lowest temperature of that
decade and again is incremented upward until the user releases the
TEMPERATURE key. In other words, each key 26a-26d is limited to its
own decade of temperatures, and cannot be used to store a
temperature falling within one of the other decades.
Once register H1 has been set, the user proceeds with setting the
next register H2. H2 is called up by pressing and releasing HEAT
SET key 20 once rapidly, and then pressing and holding HEAT SET key
20 until display 16 displays "H2", followed by the time contained
in register H2. As the user continues to hold HEAT SET key 20, the
displayed time begins to increment upward. The user continues to
hold HEAT SET key 20 until the desired time appears, and then
releases HEAT SET key 20. This causes the last time to be displayed
in display 16 to be stored in register H2. Microcomputer 57 then
causes display 16 to again display room temperature.
To set the temperature for register H2, the user depresses and
releases HEAT SET key 20 twice rapidly, thereby calling up register
H2. He then holds the desired TEMPERATURE key 26a, 26b, 26c or 26d
and holds that key until the desired temperature appears on display
16. At that point, the user releases the TEMPERATURE key, thereby
causing the temperature displayed on display 16 to be stored in
register H2.
The storing of time and temperatures in registers H3 and H4 is
achieved in a similar fashion. To access register H3 and store a
time, HEAT SET key 20 is pressed and released rapidly twice and
then held a third time until the desired time of day appears. To
store a temperature in register H3, HEAT SET key 20 is pressed and
released three times rapidly, and then one of the four TEMPERATURE
keys 26a-26d is held until the desired temperature appears.
Similarly, to store a time in register H4, HEAT SET key 20 is
pressed and released rapidly three times, and then pressed and held
a fourth time until the desired time is displayed on display 16.
HEAT SET key 20 is then released, thereby causing the displayed
time to be stored in register H4. To store a temperature in
register H4, HEAT SET key 20 is pressed and released rapidly four
times, and then one of the four TEMPERATURE keys 26a-26d is pressed
and held until the desired temperature is displayed. Upon release
of the key the displayed temperature is stored in register H4.
The user can review the contents of registers H1 through H4 by
pressing and releasing HEAT SET key 20 rapidly. Microcomputer 57
then causes display 16 to display "H1" followed by its time and
temperature; "H2" followed by its time and temperature; "H3"
followed by its time and temperature; and finally "H4" followed by
its time and temperature. Display 16 then returns to displaying
room temperature. If the user is not interested in viewing the
contents of H1, the contents of H2, H3 and H4 can be reviewed by
pressing and releasing HEAT SET key 20 twice rapidly. This will
cause "H2", "H3" and "H4" to be displayed, together with their
stored times and temperatures. Similarly, only H3 and H4 can be
viewed by rapidly pressing and releasing HEAT SET key 20 three
times. Finally, if only H4 is to be reviewed, HEAT SET key 20 is
rapidly pressed and released four times. A recall of the contents
of registers H1 through H4 can be cancelled at any time by touching
either key 18, 22 or 24.
Control of air conditioning by thermostat 10 is programmed in a
similar manner. With air conditioning, however, only a single
turn-on time and temperature may be stored. In addition, a turn-off
time for shutdown of the air conditioning system is also
stored.
The turn-on time and temperature for air conditioning is stored by
pressing and holding AC SET key 22. Microcomputer 57 causes display
16 to first display "AC", followed by the time and temperature then
stored in the AC register. As the user continues to hold AC SET key
22, time is displayed on display 16 and begins to incrementally
increase until the user releases AC SET key 22. The displayed time
at the instant when AC SET key 22 is released is stored in the AC
register.
The user then sets a temperature in the AC register by pressing and
releasing AC SET key 22, and then pressing and holding the desired
TEMPERATURE key 26a, 26b, 26c or 26d. The temperature will be
displayed on display 16, and will count upward until the
TEMPERATURE key is released. The temperature displayed on display
16 at the instant when the TEMPERATURE key is released is stored in
the AC register.
The user then sets a time in the AO register which represents the
time at which the air conditioning is to be turned off. The user
presses and holds AC OFF key 24, which causes "AO" to be displayed.
As AC OFF key 24 continues to be held, time is displayed and begins
to increment upward until AC OFF key 24 is released. The displayed
time at the instant when AC OFF key 24 is released is stored in the
AO register.
The present invention also provides for complete shutdown of the
air conditioning system, which is typical during winter months,
when air conditioning is not needed. To shut down the air
conditioning system, the user performs the same operation used to
set a time in the AO register, but continues to hold the AC OFF key
24 until the letters "OF" appear on display 16. The user then
releases AC OFF set switch 24, causing microcomputer 57 to maintain
the air conditioning system in a continuous "off" state until the
contents of the AO register are altered to remove the "OF" shutdown
setting.
To review the air conditioning settings, the user rapidly presses
and releases the AC SET key 22. As a result, microcomputer 57
causes display 16 to display "AC" followed by the time and
temperature stored in the AC register, followed by "AO" and either
the time stored in the AO register, or "OF".
An important advantage of the thermostat is the simplificity with
which the temperature and time settings are stored and retrieved. A
minimum number of keys are used, together with a "slew entry" type
of system in which the keys are held until the desired time or
temperature setting is displayed. The keys or switches must be held
for a certain predetermined time, such as six seconds, before any
alteration of the contents of the registers are effected. As a
result, an accidental contacting of the keys will not result in
accidental alteration of stored time and temperature settings.
Another important advantage is that microcomputer 57 automatically
sorts the time settings within the registers H1 through H4. The
user may enter times and temperatures in any order, and need not
place the earliest time in register H1. This is an important
advantage, particularly where the user wishes to add an additional
time and temperature (where at least one of the registers had not
been previously used), or wishes to alter the time and/or
temperature setting stored in one of the registers. Unlike prior
art digital clock thermostats, the thermostat of the present
invention does not require that the user reprogram all of the
temperature and time settings in order to place the times and
temperatures in sequential order. Rather, microcomputer 57
automatically sorts the times within registers H1-H4 to place them
in sequential order for use in controlling the heating system.
In normal operation, microcomputer 57 causes display 16 to display
room temperature, as sensed by thermistor 94. On a periodic basis,
which in one preferred embodiment is every minute, microcomputer 57
performs an "update" routine in which it determines whether the
furnace should be turned on or off, and whether the air
conditioning should be turned on or off. Unlike prior art digital
thermostats, the preferred embodiment of the present invention
automatically decides whether to turn on heat or air conditioning,
and does not require the user to select heating only or air
conditioning only.
When microcomputer 57 begins the update routine, it first
determines the room temperature from the room temperature register,
and then determines the time of day from the time-of-day register.
Microcomputer 57 then compares the time of day from the time-of-day
register with the times stored in registers H1, H2, H3 and H4, in
order to determine which of the four registers is applicable.
After the proper heat register (H1-H4) has been selected,
microcomputer 57 compares the sensed room temperature with the
control temperature in the selected heat register. Depending upon
this comparison, microcomputer 57 may provide a signal to control
circuit 82 to (a) turn on the furnace if it is presently off; (b)
turn off the furnace if it is presently on; (c) leave the furnace
on; or (d) leave the furnace off. If the furnace is to be turned
on, turned off, or left on, microcomputer 57 takes the appropriate
action and discontinues the update routine. If, however, the
furnace was already off and the decision was made that it should
remain off, microcomputer 57 then checks the contents of the AO and
AC registers to determine whether air conditioning is
appropriate.
If the content of the AO register is "OF", no air conditioning is
permitted and microcomputer 57 discontinues the "update" routine.
If, on the other hand, the content of the AO register is a number
between "00" and "23", microcomputer 57 then checks the time stored
in the AC register against the time of day. If this comparison
indicates that air conditioning should be on, microcomputer 57 then
compares the room temperature to the control temperature stored in
register AC and provides the appropriate signal to control circuit
94 to control the air conditioning system. Microcomputer 57 may (e)
turn air conditioning on, (f) turn air conditioning off, (g) leave
air conditioning on, or (h) leave air conditioning off.
If the time of day does not fall within a time period in which the
air conditioning is to be operating, as indicated by the times
stored in the AO and AC registers, microcomputer 57 normally will
not turn on the air conditioning. If, however, the room temperature
exceeds a predetermined level, such as 85.degree. F., and the AO
and AC registers indicate that air conditioning is desired during
some hours of the day, then microcomputer 57 will provide signals
to control circuit 94 in order to operate the air conditioning
system to maintain room temperature at 85.degree. F. In this way,
room temperature is not permitted to rise to such a high level that
the air conditioning would be unable to effectively reduce the room
temperature to the desired control temperature during the time
period when air conditioning is desired.
The thermostat of the present invention also prevents undue
switching back and forth between heating and air conditioning by
giving first priority to heating. Microcomputer 57 always checks
the contents of registers H1-H4 first, and controls the furnace
before any determination of the need for air conditioning is made.
In addition, the need for air conditioning is checked by
microcomputer 57 only if the furnace is already off and the
decision (by comparing the room temperature with the control
temperature in one of the heat registers (H1.varies.H4) is that the
furnace should remain off. As a result, a time delay of at least
one minute (the period between successive "update" routines) occurs
between the turning off of the furnace and the turning on of the
air conditioner. If microcomputer 57 turns off the furnace during
one update routine, it must wait until the next update routine
before it can determine the need for air conditioning.
The thermostat of the present invention, therefore, provides
automatic control of both heating and air conditioning and an
automatic switch-over between heating and air conditioning without
requiring the user to change the position of a switch. This is
particularly advantageous in climates where there is wide variation
between daytime and nighttime outdoor temperatures. In these
climates, it is often necessary to provide air conditioning during
the day and heating during the night.
In addition, the information stored in registers H1-H4 is
independent of the information stored in registers AO and AC. The
programming of heat control information in registers H1-H4 is
independent of and does not affect the information in registers AO
and AC, and vice versa. When the thermostat automatically switches
between heating and air conditioning, the contents of registers
H1-H4, AO and AC remain intact. This is unlike the prior art
digital thermostats in which switching between heating and air
conditioning requires reprogramming and/or results in a loss of the
time/temperature program for either heating or air
conditioning.
In conclusion, the present invention is an easy-to-use, low cost,
digital clock thermostat. Although the present invention has been
described with reference to preferred embodiments, workers skilled
in the art will recognize that changes may be made in form and
detail without departing from the spirit and scope of the
invention.
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